The present invention relates to apparatus for controlling the power applied to a load from a source and, more particularly, to a novel temperature-responsive circuit for causing load control apparatus to reduce the load power when a predetermined temperature is exceeded.
It is well known that all energy-conversion apparatus is somewhat less than perfect, i.e. that the magnitude of output energy, in the desired form, is always less than the magnitude of the input energy form, with the lost energy difference typically being dissipated from the energy conversion apparatus as heat energy. For example, if the apparatus is designed to convert electrical energy to light energy, i.e. a lamp, a portion of the input electrical energy is lost as dissipated heat. The temperature produced in the vicinity of the energy converter, by this dissipated heat energy, is highly dependent upon the design of the enery-converter (the lamp), the ambient temperature, and other factors, such as lamp orientation (e.g. lamp base up or lamp base down) and the like. The dissipated heat energy problem is particularly exacerbated in loads requiring the placement of load-control electronic apparatus in close proximity to the load/dissipated heat source. For example, a lamp operating at an average voltage less than the average AC line voltage, by action of lamp power-control apparatus interposed between the AC line and the lamp itself, will typically have the electronic power-control apparatus located adjacent to the lamp base, whereby the power-control electronic apparatus is affected not only by the energy loss therein but also receives a significant portion of the heat energy dissipated by the lamp during the course of the operation of the latter. It is highly desirable to prevent the electronic control apparatus from reaching an excessive temperature, while still permitting the electronic control apparatus to maintain the functionality of the light source with minimum application restrictions. Thus, it is particularly desirable to prevent damage to the load power-control electronics while maintaining a reduced load energy (light) output especially if normal cooling is reduced or the load is improperly positioned. Similarly, it is equally desirable that the full converted-energy (light) output can be reestablished when the load power-control electronics apparatus cools to a temperature below a predetermined maximum safe operational temperature.